block heater

[Jerry/MT]

Yes and no. Wind chill on skin is related to evaporation of moisture in the skin--as water (liquid) evaporates, it removes heat. No matter how dry your skin feels, there is still water present to evaporate.

Your engine block has no water to evaporate into free space the way your skin does. Still, as the block warms, it warms the air around it. If the air is still, that "bubble" of warm(er) air will draw less heat from the engine than cold air (rate of heat exchange is proportional to the difference in temperature). Blow away that warmer air and replace it with cold and you'll lose heat faster, resulting in a lower block temperature and longer preheat times.

"Wind chill" is determined by heat transfer rate (BTU/sec) not temperature. Any heated body will lose heat faster when there is air blowing over it than it will when the air speed is zero. It's the difference between natural and forced convection. That heat loss rate makes you "feel" colder than just the static temperature. It doesn't mean your temperture is colder.

So if a heated body ( i.e a human, a tractor with the block heater on, a warmed up tractor with an engine that's shut off) transfers 10 BTU/sec at 10°F ambient temperature with no wind velocity and also transfers 10 BTU/sec at 40°F with a 20 mile an hour wind, then the combination of 40°F temperature and the 20 mph wind gives a wind chill of 10°F. (I just made these numbers up to illustrate the point. Go to the wind chill charts to get the correct windchill verus wind speed and temperature.)

Certainly the body being cooled will not get colder then Tstatic + recovery factor *(V^2/2gJcp) but it will most certainly lose heat at a faster rate with inreasing wind speed.

To answer the original question I have a timer on my block heater and it's set to go on 2 hrs before I feed the cows. It's overkill for temperatures above 20F but it's needed for -20F.

 

[irvingj]

Bingo, Jerry!:thumbsup:

 

[DarrylH20]

Bingo, Jerry!:thumbsup:

This would be good for Myth Busters to figure out

 

[Don87]

Wow........what can I say, you apparently don't understand

So much wrong information in your last post........it isn't even funny.

I had to go to work on Sunday, I should have posted that I was leaving.

But, Yes you said things that were totally wrong because you got into assuming things.

First was the truck, It was 20 years ago when it happened( so exact details are a little fuzzy).

My boss told him the same thing that I've stated here.

But, when I got to the truck stop, he had the exact same argument as you "wind chill can not affect the filters". So I changed the filters, and headed for the shop (9 miles away).
He called the shop before I got back there. Gelled again, this time on the interstate. He didn't argue anymore.

The temperature at this time was cold, but not cold enough to gel fuel on a standing vehicle.

Second part of your post..

The bridge, again you were assuming conditions that did not exist.
Temperature that day had a high of 50 degrees.
There was a big cold front coming in, and the wind kicked up to 30mph.

The temp was 40 when I came to the bridge. The large creek under the bridge was frozen solid, wind direction was perpendicular to the bridge.

Bridge was frozen.

But what amazes me the most about all this, is that there have been quite a few people in this thread that have experienced the 'wind' effect on their vehicle. And the response has been 'the book says it can't happen, therefore it didn't'

 

[Don87]

This would be good for Myth Busters to figure out

Mythbusters lost my faith with the episode that had the 2 tractor trailers with 1 car in the middle.
The 'myth' was that in a head-on collision between 2 trucks, the car would become part of the truck.

On the actual trial that they did, the truck on the left of the screen hit the car, a split second ahead of the the truck on the right, causing the car to turn slightly. Truck 2 did not hit the car square, thus pushing the car clear.
They ruled the story a myth based on an 'innacurrate test'.

 

[AKwelder]

just came south of the arctic circle, work has had me up to 300 miles NORTH of the arctic circle. There are no trees, wind breaks or anything warm including the sun.

It was 58 below zero, and then there was a 20 some MPH wind. I was cold, I mean COLD. Every BTU you add, AND KEEP, helps. So where as the ambient temperature does not affect things, the amount of heat loss does.

if you need to heat a motor you also heat the area and air around it, the metal motor conducts heat to the air. So if the air around the motor is constantly exchanged, the motor can expend heat (BTU's) to heat it.

 

[Don87]

just came south of the arctic circle, work has had me up to 300 miles NORTH of the arctic circle. There are no trees, wind breaks or anything warm including the sun.

It was 58 below zero, and then there was a 20 some MPH wind. I was cold, I mean COLD. Every BTU you add, AND KEEP, helps. So where as the ambient temperature does not affect things, the amount of heat loss does.

if you need to heat a motor you also heat the area and air around it, the metal motor conducts heat to the air. So if the air around the motor is constantly exchanged, the motor can expend heat (BTU's) to heat it.

You could be right, as well as several other people have posted on here.

The only thing I know for sure is that the wind will have an adverse affect on an engine, if it blows into the front of the vehicle, and said vehicle has a radiator in the front(haven't tested my MF with the reverse mounted engine).

I have no clue as to whether the 'liquid' inside the 'inanimate' object makes a difference, but it would 'appear' that it may.

I for one refuse to rule anything out, because Mother Nature, tends to prove humans wrong time and time again.

 

[Don87]

And I'll post my plans now........I must leave my house by 10 am Sunday, 12/19/10.

Load must be in Aurora, Il. by 7 am(CST). 12/20/10.

 

[brokenot]

First was the truck, It was 20 years ago when it happened( so exact details are a little fuzzy).

My boss told him the same thing that I've stated here.

But, when I got to the truck stop, he had the exact same argument as you "wind chill can not affect the filters". So I changed the filters, and headed for the shop (9 miles away).
He called the shop before I got back there. Gelled again, this time on the interstate. He didn't argue anymore.

The temperature at this time was cold, but not cold enough to gel fuel on a standing vehicle.

I'll ask again because the question still hasn't been answered. If a truck jells up, and you do nothing to it other than swapping out the filters, what have you done to fix the problem?

If the ambient temperature hasn't changed, and the road speed of the truck hasn't changed, then as soon as the truck hits the road again, the same jelling will occur if "wind chill" is causing it. It makes no difference if it's tomorrow or next week, if it was "wind chill" that jelled the fuel, then "wind chill" will jell it again as soon as those same, (or more severe), "wind chill" conditions are re-created. What happens in your scenario if the truck jelled at 50 mph initially and you then swapped the filters, and when he hits the road again he ramps it up to 70 or 80 mph? Your "wind chill temperature" just took a significant nose-dive.

The last sentence in your quote is what this entire discussion is about in my opinion.

The temperature at this time was cold, but not cold enough to gel fuel on a standing vehicle.

If fuel jells at "X" temperature, then that's it. That jelling temperature is actual. Wind chill isn't actual, and it's extremely easy to demonstrate. Take a fuel sample and set it on your hood or roof when the ambient temperature isn't cold enough for the fuel to jell. Then find a safe section of roadway and see if you can go fast enough to create enough "wind chill" for it to jell.

But what amazes me the most about all this, is that there have been quite a few people in this thread that have experienced the 'wind' effect on their vehicle. And the response has been 'the book says it can't happen, therefore it didn't'

That's because, (no offense intended here), many examples are more along the lines of "it seemed like...."

For example, the first time you posted up about the truck jelling example, here's your exact quote:

I can't count the number of tractor trailers that I had to do road service on because they were froze up and they were driving down the highway when it happened. Was running fine when they left the truck stop at Keysers Ridge, Md., but it froze up while moving.......you have yet to explain it.

This is your last post on the truck situation:

First was the truck, It was 20 years ago when it happened( so exact details are a little fuzzy).

Notice any difference there? We went from a number or trucks that's too great to keep track of, to "the truck", and it "was 20 years ago when it happened".

 

[BeeferMan]

This thread is amazing!

It's really quite simple - think about it as the transfer of heat. In order to cool something to say, zero degrees, you need a heat sink that is at least zero degrees to absorb the heat. You cannot cool anything to a temperature lower than your heat sink. (I think we can ignore magnetic cooling techniques here.) If air is your heat sink, and that heat sink is zero degrees, you cannot cool anything to a temperature less then zero degrees. It does not matter if your heat sink is moving or static, you cannot cool anything to a temperature lower than your heat sink.

Moving air or water will cool something faster (read: remove heat faster) than stationary air or water, but it will never cool that object to a temperature lower than the temperature of the stationary air/water.

If it helps, think of the opposite situation - heating something. If you have a heat source, is it possible to heat something to a temperature higher than your heat source? Of course not.

Conclusion: so called "wind chill" will cool an object faster than still air by removing heat faster, but it will not ultimately cool it to a lower temperature than still air.